Process for the manufacture of products from reinforced polyester resins

ABSTRACT

A process for the manufacture of glass fiber-reinforced polyester products is disclosed. A ready-to-mold resin and reinforcement composite is prepared using an initiator which has been microencapsulated in order to prevent initiator-induced cross-linking of the resin reactants. The initiator is released during the molding of the composite by rupture of the microcapsules due to internal vapor pressure developed at a preselected molding temperature. The encapsulation of the initiator provides improved homogeneity and increased flowability of the composites during molding, and enables the provision of molded polyester products having higher degrees of cure and more defect-free finish surfaces.

This application is a continuation-in-part of application Ser. No.441,385, filed Nov. 12,1982, now abandoned, and of Ser. No. 510,596,filed July 5, 1983.

BACKGROUND OF THE INVENTION

This invention relates to a process for the manufacture of products fromreinforced polyester resins and, more particularly, polyester resinsystems which are reinforced with glass fibers. In accordance with theprocess, encapsulated reaction additives such as initiators remainfunctionally isolated in the blended molding materials until released bypreselected process conditions. Products manufactured from reinforcedpolyester resins are widely used in automotive, appliance, and otherindustries.

In the processes now employed, polyester resin reactants are added to alarge mixer along with the additives, such as promoters or accelerators,inhibitors, pigments, stearates, fillers, thermoplastic profilingcompounds, and the initiator or catalyst. The material is intensivelymixed with high energy shearing for perhaps 20 minutes and then it ismade into sheet molding compound (SMC), thick molding compound (TMC) orbulk molding compound (BMC).

With SMC, the reinforcing glass fibers are of variable length and areintroduced as the mixture of resin and additives is disposed betweensheets of protective polyethylene film. Optionally, continuous lengthsof glass fiber roving or mat may be disposed between sheets of compound,which in turn are covered, top and bottom, with protective polyethylenefilm. The film-protected SMC composite is passed between rollers whichknead the composite in order to thoroughly mix and wet the glass fiberwith resin reactants. The SMC is up to perhaps 1/4 inch thick. There arespecial high strength forms of SMC based upon particular fiberglassreinforcement characteristics. The TMC comes in sheet form like SMC, butmay be up to several inches thick.

With BMC, short glass fibers 1/8 to 1-1/4 inches long are thereinforcement and are added at the time of mixing. BMC has a consistencysimilar to that of modeling clay and is extruded into logs or ropes, orpelletized, or may be used right out of the mixer.

The ready-to-mold resin and reinforcement composites in the form of SMCand BMC materials are made up intermittently in large batches inaccordance with production demand. After mixing, they are stored undercontrolled conditions until they are used. Because the initiator ismixed into the compound, the compounds are partially cured and gelled,which increases their viscosity, and they continue to cure slowly instorage. After one or two months in storage, they become too cured orviscous to use and must be discarded. They thus have limited shelf life,depending upon storage conditions.

In the course of the mixing, the temperature increases because of theenergy put into the compound and because the reaction is exothermic. Theintensity and length of the mixing process must be restricted to avoidexcessive premature cure of the compound. Water jacket coolingtechniques may be employed, but the mixing operation remains an art withvariation of resin materials and initiators, as well as the possible useof promoters or accelerators and inhibitors. Often, the mixing processis simply terminated just prior to a critical temperature (e.g., 32°C.).

One problem with SMC and BMC materials is that because of the restrictedconditions under which they are mixed, it often happens that theinitiator and fillers are not completely distributed throughout themixture. This frequently occurs if the temperature of the mixtureincreases too much and the mixing operation has to be cut short beforethe additives are completely mixed in.

SMC is, for the most part, molded in matched metal die compressionmolds. It usually is about 24 inches wide and is weighed and cut intosuitable lengths for insertion into the molds. BMC is likewise molded incompression molds. Pieces of BMC are cut off by weight and placed intomolds. Charges can weigh as much as 30 pounds or more. BMC can bepreheated in a screw and injected into the mold. It can also beinjection-molded with a plunger. SMC, TMC, and BMC materials can also bemolded in transfer molds. At this writing, most production uses eitherSMC or BMC compounds. The use of TMC is limited.

It is desirable for cost purposes to minimize the molding cycle or time,which tends to increase with the weight of the charge to the mold. Tothat end, increased amounts of initiators are used in combination withinhibitors, which act as free radical traps and tend to preventpremature initiation of polymerization. Preferably, the effect of theinitiator is depressed during the storage of the compounds to improveshelf life, as well as during the mold filling process. However, at thedesired point of cure, the initiators should cause rapid cure at hightemperatures. Heretofore, these ideal conditions have been soughtthrough the use of combintions of initiators and inhibitors, as well aspromoters or accelerators, which tend to lower the decompositiontemperature of the initiator. Combinations of these reaction additivesinvolve trade-offs in the physical properties of the cured resin.Further reference is made to U.S. Pat. No. 2,632,751, columns 1 and 2.

For the products molded from SMC and BMC materials, there have alwaysbeen problems in filling the molds completely and in obtaining suitablesurface finish of the molded parts, even though inhibitors are used todelay the curing reaction and viscosity increases. From 10-20% of theproducts so molded have to be hand-finished, which is expensive andtime-consuming. Even with hand-finishing, the scrap rate for thesemolded products may be in the order of 50%. The molded products areusually painted, but they have to be washed and cleaned before they canbe painted. In both the cleaning and painting steps, the products areheated back up to temperatures which approach those at which they weremolded. Most products are between 85% and 90% cured when they come outof thee compression mold. The heating from the washing and paintingincreases the degree of cure, but also relieves stresses in the parts,causing warpage and distortion.

Curable resin compositions containing encapsulated catalysts are known.U.S. Pat. No. 3,860,565 teaches the encapsulation of the catalysts forisocyanate resins and identifies a number of other patents relating tocurable resin systems with encapsulated catalysts. So far as I know,however, no one has ever taught or suggested the encapsulation of theinitiators or catalysts in polyester resin systems. These initiators areusually organic peroxides in the form of volatile liquids. Suchinitiators are toxic and difficult to handle.

The processes for the micro-encapsulation of materials are well known,and have been well known ever since the end of World War II. Referenceis made to "Microcapsule Processing and Technology," Asaji Kondo, editedand revised by J. Wade Van Valkenburg, Marcel Decker, Inc., New YorkN.Y. (1979), and "Capsule Technology and Microencapsulation," Noyes DataCorp., Park Ridge, N.J. (1972).

SUMMARY OF THE INVENTION

I have discovered that initiators for polyester resin systems can beencapsulated in rigid microcapsules so as to permit them to bethoroughly mixed into the SMC or BMC materials in the mixing processwithout breaking, and then be released when the materials are molded.The microcapsules are substantially inert to the components of theready-to-mold resin composites and serve to isolate the encapsulatedadditive from reaction with the components. The capsule shell walls arestrong enough to retain their integrity throughout the mixing process,but rupture and release the initiator at predetermined moldingtemperatures and pressures. The internal vapor pressure of theencapsulated material at the molding temperatures is believed to rupturethe capsules, releasing the initiator.

The use of thermosetting resin such as phenolic resin to encapsulateorganic peroxide initiator has been found to provide satisfactoryreaction isolation and structural integrity in polyester systems. Thephysical characteristics of the microcapsule are matched with thecharacteristics of the particular organic peroxide initiator andpolyester resin system to provide capsule rupture and release of theinitiator at a temperature close to the molding temperature of thesystem.

SMC and BMC materials with my encapsulated initiator have greatlyextended shelf life. Viscosity stability has been maintained for overtwo months in typical composite formulations. The resins have improvedmolding properties. Hand-finishing and the scrap rate are reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph displaying the temperature-versus-time profiles forthe molding of an SMC composite, with and without initiatorencapsulation, in accordance with my invention; and

FIG. 2 is a thermogram for an encapsulated initiator.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to any of the conventional polyester resinsystems which are used to make SMC and BMC materials. These areunsaturated polyester resins, typically the condensation product of amixture of an unsaturated dibasic acid and a saturated dibasic acid anda glycol. The proportions of saturated and unsaturated dibasic acids arevaried depending upon the desired properties of the molded compound,such as flexibility, hardness, heat resistance, and the like. The usualcross-linking monomers are styrene or vinyl toluene. The usualinitiators or catalysts are free radical initiators such as organicperoxides which decompose with heat to provide free radicals. Althoughthey are often called catalysts, they are, strictly speaking, initiatorsbecause they are used up in the reaction.

Various kinds of fillers are added, such as calcium carbonate, clays,talcs, and the like. Other additives are ultraviolet absorbers, flameretardants, antioxidants, mold release agents, and the like, all as arewell known in the art.

Additional description of polyester resin systems appears in U.S. Pat.No. 4,053,448, columns 2-4.

In accordance with my invention, the initiator is encapsulated inmicrocapsules. The microcapsules of this invention may range in sizefrom 5 to 200 microns. Satisfactory results have been achieved hereinwith microcapsules ranging from 10 to 50 microns in diameter or size.The encapsulating materials are preferably phenol-formaldehyde resinswith physical characteristics, particularly wall thickness and rupturestrength, designed to withstand the internal vapor pressure of theencapsulated material up to the pressures developed at the moldingtemperatures of the SMC or BMC materials. At the molding temperatures,the capsules rupture and release the initiator. At the same time, thecapsules are small enough and strong enough so that they can withstandthe intensive mixing which is required to form SMC or BMC materials andnot release the initiator.

The encapsulating resin and the wall thickness of the capsules areselected to provide rupture at the desired temperature and pressure. Asshould be obvious, the rupture strength of the resin varies with theresin material and composition. Likewise, thin capsule walls rupturemore easily than thick capsule walls. In accordance with my invention,these factors are correlated with vapor pressure to provide rupture atthe desired temperature. Molding temperatures are typically in the orderof 138° to 177° C., depending upon the initiator. Satisfactory rupturetemperatures range from about 30° C. and, more preferaby, from about 10°C. below the molding temperature to about the molding temperature orfrom about 20% and, more preferably, from about 10% below the moldingtemperature to about the molding temperature.

The internal vapor pressure for rupturing the microcapsules is developedupon heating of the encapsulated material which preferably includes aliquid phase. The liquid phase may comprise the initiator, a solvent forthe initiator, or a diluent for the initiator, or such other liquidphase as may be present within the microcapsule in a form compatiblewith the initiator.

Following rupture and release of the initiator, the fractured sectionsor residue of the ruptured capsule wall remain in the composite andmolded thermoset product. These fractured sections, which are believedto be fragments of spheres, have not been found to interfere with theprovision of commercially acceptable appearance surface part of a ClassA surface molded part. Similarly, the potential occurrence ofmicrocapsule (or agglomerated microcapsules) rupture at the surface hasnot been found to give rise to visual or physical surface defects.Contrarily, my encapsulation techniques have resulted in improved andmore defect-free finish surfaces on the molded part as indicated aboveand demonstrated hereinafter.

Inhibitors are not generally required for the practice of my invention.Encapsulation of the initiator tends to increase the effectivedecomposition temperature of the particular initiator in a mannerdifferent from that encountered in the use of inhibitors, which reactwith the first free radicals produced. The encapsulation technique of myinvention permits one to increase the molding temperature by at least15%, and thereby allow the mold cycle time to be reduced. Highertemperatures are believed to contribute to the increased degree of cureobserved in the use of encapsulated initiators.

There are many advantages which result from the use of my invention.Because the initiator does not interact with the resin until it isreleased from its capsule, there is very little pre-curing of the resincomponent in the composite. The composites can be mixed for longertimes, at higher temperatures of up to 65° C. or more, so that there isa more homogeneous mixture. When molded, the flow into the mold isexcellent, so that the composites completely fill the mold and areotherwise readily molded. The composites have a shelf life limited bythe shelf life of the resins. The need for free radical curinginhibitors is eliminated. The initiator, fillers, and other additivesare more evenly distributed throughout the composite because one can mixfor longer times and at higher temperatures. The improved distributionof the encapsulated initiator is most surprising, since prior arttechniques often required dissolving the initiator in a solvent prior toits addition to the composite. Upon curing the composites to providepolyester resin thermoset products, there is increased cross-linking,thus improving dimensional stability and reducing warpage in subsequentwashing and painting steps.

Another advantage of my invention is that I do not require promoters oraccelerators in order to achieve suitable cure or cross-linking. With myinvention, without any promoter, I can achieve cures of at least 85% andpreferably up to 95% as measured on a Perkin-Elmer differential scanningcalorimeter. Moreover, for all except unusually large parts, the moldingtime is usually less than 3 minutes, and for many parts is less than 1minute.

Additional advantages may be obtained by the use of combinations ofseparately encapsulated, different initiators, as well as mixingdifferent initiators in the same capsules. Also, less than all of theinitiator may be encapsulated so as to allow precise control of theamount of initiator available for initial gel and viscosity buildup inSCM applications, for example. Further, a nonencapsulated initiatorhaving a relatively low half-life temperature may be used to effect geland viscosity buildup and combined with an encapsulated initiator havinga high half-life temperature to effect high temperature, more completecure of the molded product.

The organic peroxides which may be encapsulated in accordance with myinvention include any of the wellknown diacyl peroxides, peroxyesters,dialkyl peroxides, and peroxyketals. A suitable diacyl peroxide isBenzoyl Peroxide. Suitable peroxyesters are t-Butyl Peroctoate andt-Butyl Perbenzoate. A suitable dialkyl peroxide is di-t-Butyl Peroxide.Suitable peroxyketals are 1,1,bis(t-Butyl Peroxy) Cyclohexane and1,1,di-t-Butylperoxy 3,3,5 Trimethyl Cyclohexane. All of theabove-listed organic peroxides are liquids except for benzoyl peroxide,which must be put into solution in a suitable solvent such as styrenebefore being encapsulated. The organic peroxide initiators are freeradical initiators.

The preferred materials for encapsulating the initiator arephenol-formaldehyde resins. These resins have been found to beparticularly suitable for encapsulation of t-Butyl Perbenzoate,1,1,bis(t-Butyl Peroxy) Cyclohexane and 1,1,di-t-Butylperoxy 3,3,5Trimethyl Cyclohexane. Other unsaturated thermoset resins may be used,such as polyester resins, urea-formaldehyde, and melamines. Theencapsulating material should be inert, relatively brittle, andimpervious to the initiator so as to keep it separate from the polyesterresin until it is released.

Although glass fibers are the usual reinforcing materials, I contemplatethat my invention can be used with other reinforcing materials such ascotton, metal filaments, synthetic fibers, carbon and boron fibers, andthe like.

EXAMPLE 1

Comparative tests were made between an SMC composite including anencapulated initiator in accordance with my invention and an otherwiseidentical composite incorporating the same initiator in a conventionalmanner without encapsulation. The SMC composites were used to mold acurrent model automobile grille opening panel. The panel comprises theforward body component in which the grille and headlights are mounted,and it was selected because it is a difficult part to mold and itincludes a substantial expanse of finished surface.

The resin system employed in the composite was an Owens-CorningFiberglas automotive grade polyester resin identified as OCF CX 1248,which is a di-cyclopentadiene maleate polyester in styrene monomer witha vinyl acetate acrylic additive as low profile agent. The initiator wast-Butyl Perbenzoate (TBPB). A promoter designated Pep 308 sold by AirProducts and Chemicals of Allentown, Pa. was used in the resin system.

The nonencapsulated initiator was added to the resin system of thecontrol composite in a conventional manner. Accordingly, the initatorwas added directly to the mixer containing the polyester resin systemand mixed to a temperature of approximately 32° C.

The initiator was encapsulated in a phenolformaldehyde resin and wasmanufactured by Capsulate Systems of Fairborn, Ohio, where it isidentified as PLASTICAP T. The same amount of encapsulated initiator wasused as in the control composite with allowance for the weight of theencapsulating material. The encapsulated initiator was added to theresin system of the test composite prepared in accordance with myinvention by direct addition to the mix as the resin forming componentswere blended. In this instance, mixing was allowed to continue until atemperature of approximately 57° C. was reached, since encapsulation ofthe initiator allows higher mixing temperatures to be used withoutcross-linking occurring.

The SMC composites were matured for three days to allow for suitableviscosity buildup in accordance with conventional molding procedures.Thereafter, approximately 15 grille opening panels were molded in acompression mold at 160° C. using each of the SMC composites.

The parts molded using the nonencapsulated initiator were badlypre-gelled, and there was excessive porosity. The parts were washed andpainted. Upon inspection, the parts were commercially useless, due totheir unacceptable appearance and extensive rework would have beenrequired to make them usable.

subsequently, in the same mold at the same temperature, the SMCcomposite prepared using the encapsulated initiator was used to preparethe test grille panels. On inspection of the molded parts, the pre-geland porosity were found to have been greatly reduced. The parts werewashed and painted, and at least 90% of the parts were commerciallyacceptable without rework.

The improved flow and moldability of my invention thus provides a muchlower scrap rate and reduced amount of hand-finishing. The surfacefinish is of excellent quality, substantially free of pre-gelimperfections, and ripple is reduced.

EXAMPLE 2

In further comparative tests using SMC composites with and without myencapsulation techniques, automotive spoilers were prepared usingmatched metal die compression molding. Once again, an automotive gradepolyester resin system was used, it being identified as TP 40139,P340/LP40A system. This is a propylene maleate polyester in styrenemonomer with a low profile additive. The initiator was TBPB. The SMCcomposites were prepared and matured in the same manner as in Example 1.For purposes of comparison, 80 spoilers were molded at a moldtemperature of 160° C., using each of the SMC composites.

The appearance surfaces of the molded parts were inspected to determineporosity defects. A porosity defect is a pinhole-sized physical openingin the part requiring rework to make the part commercially acceptable.The parts prepared in a conventional manner without encapsulation of theinitiator averaged 15.4 porosity defects per part. The parts preparedwith the identical SMC composite but for the encapsulted initiatoraveraged 1.4 porosity defects per part. Obviously, the amount ofpatching rework was substantially reduced, and production economies wereachieved.

The improvements obtained using may encapsulated initiator are believedto be related to the improved homogeneity and increased flowability orflow time of the composites during molding. The latter property isdemonstrated by use of a spiral flow test which determines the flowproperties of the composite based on the distance it will flow along aspiral runner of constant cross section under controlled conditions ofsample weight, pressure, and temperture. The test is usually performedwith a transfer molding press and a test mold into which the compositematerial is fed at the center of the spiral cavity. (See "Whittington'sDictionary of Plastics," Lloyd R. Whittington, Technomic Publishing Co.,Inc., Stamford, Conn., 1968.)

The composites of Example 2 were tested using the spiral flow method.The composite having an encapsulated initiator had a spiral flow valueequal to 20.5 inches, and the conventional composite including anonencapsulated initiator had a value of 9.8 inches. The differences inthe test values are believed to result from the delay of thecross-linking reaction by encapsulation of the initiator. The initiatorremains isolated and initiator-induced cross-linking does not occuruntil the capsule ruptures and the initiator is released. In contrasttherewith, the nonencapsulated initiator induces preliminarycross-linking sufficient to impede the flowability of the composite.

The temperature-versus-time profile for the molding of the SMCcomposites of Example 1 were determined, using techniques similar tothose described in "Curing of Compression Molded Sheet MoldingCompound," Ly James Lee, published in Polymer and Engineering Science,Mid-June, 1981, Vol. 21, No. 8. Accordingly, identical multiple-layertest samples of the SMC composites were prepared. Each of the sampleshad a circular configuration and a total thickness of about 1.65 cm.Thermocouple wires were disposed at evenly spaced locations throughone-half the thickness of each sample, one thermocouple wire beinglocated at a surface of the sample, one at the thickness midpoint, andtwo further thermocouple wires being evenly spaced therebetween. Each ofthe samples was molded at 157° C. and the temperatures of the variousthermocouple probes were monitored. The temperature-versus-time profilefor the mid-thickness thermocouple wire for each of the composites isshown in FIG. 1.

The profiles of FIG. 1 includes initial portions or zones during whichthe temperature increases are mainly due to the heat input from themold. Thereafter, a rapid temperature increase occurs over a secondportion or zone of each of the curves during which the temperatureincrease is caused by the exothermic heat generated during the fast freeradical polymerization. It is estimated that about 90% of the totalcross-linking occurs during this exothermic portion or zone of theprofile. In a final negatively sloping portion of the profile cruve,heat transfer from the hot composite to the mold occurs.

The encapsulation of the initiator has been found to delay the beginningof the exothermic portion of the molding cycle. Herein, the beginning ofthe exothermic portion of the cycle was delayed from about 135 secondsof about 185 seconds as measured from the beginning of the mold cycle.This extends the portion of the mold cycle, during which the compositehas good flowability properties, which in turn enables improved fillingof the mold cavity and improved product surface quality.

The delay of substantially all initiator-induced cross-linking prior tocapsule rupture permits a more optimized molding cycle, since thecomposite tends to display a high level of flowability throughoutsubstantially the entire time period preceding the onset of theexothermic portion of the cycle. In this manner, early cross-linking inaccordance with the temperature-promoted disassociation of organicperoxide initiators does not occur, due to encapsulation of theinitiator. Thus, the portion of the molding cycle time allotted to thefilling of the mold cavity may be more efficiently and reliably utilizedby the molder. Accordingly, the molding temperature can be increased inorder to shorten the molding cycle.

The delay of the exothermic portion of the molding cycle by myencapsulation technique also enables the molding of rapid cross-linkingresin and initiator systems which heretofore could not be molded withacceptable commercial production consistency and quality.

In illustration of the precision of initiator release in accordance withtemperature, the encapsulated initiator used in the foregoing Examplewas subjected to thermogravimetric analysis (TGA), and the TGA resultsare presented in the graph of FIG. 2.

In this analysis, a test sample of encapsulated initiator is heated andthe sample weight change is recorded as the temperature increases.Herein, the vaporization of the liquid initiator ruptures themicrocapsule and the primary weight change is a result of the loss ofthe vaporized initiator from the test sample.

As shown in FIG. 2, a relatively small change in weight is initiallyexperienced as the test sample loses any residual moisture and, perhaps,a limited number of structurally imperfect capsules rupture and allowvaporization of the initiator. The total weight change is about 7% asthe sample is heated to temperatures in excess of 140° C.

At a temperature of about 146° C., significant, if not all, microcapsulerupture begins and substantially all of the rupture is completed as thetemperature approaches 150° C., with a small amount of rupture and/orvaporization of residual liquid initiator being completed at atemperature of up to 157° C. The percent weight change between 146° C.and 157° C. is about 82%. This is in close agreement with theapproximate 85% by weight core material fill of liquid initiator whichwas sought in the encapsulation process. The 11% weight remainder is thephenolic material of the capsule wall.

As shown in FIG. 2, the microcapsule structure is sufficiently uniformto permit substantially all of the initiator to be released within anarrow predetermined temperature range with the use of the internalvapor pressure to rupture the microcapsules. As noted above, the rupturetemperature may be varied in accordance with the properties of theencapsulation wall material and initiator.

As used herein, the phrase "ready-to-mold resin and reinforcementcomposite" or abbreviated forms thereof comprehend SMC, TMC, BMC, andother similar premixed, fiber-reinforced molding compounds made withintensive mixing from polyester resin systems which require a freeradical initiator. Such molding compounds have an initial viscosity,that is, the viscosity after mixing but before aging, of 40,000 to80,000 centipoises at 22° C. (Measured with a Brookfeild "HBT Model"viscometer, at 5 rpm's using a number 6 spindle.) After aging, theviscosity should be at least 60,000,000 centipoises and up to 80,000,000centipoises at 22° C. (measured at 1 rpm, using a TF spindle). Theseviscosity characteristics are for SMC resin control samples free offiber reinforcement and thickeners. Corresponding viscosity controlmeasurements are not typically made for BMC or TMC resin materials, butit is believed that similar viscosity values exist. Thus, after aging,the control viscosity for the compond should be at least 60,000,000centipoises.

The terms "mold" and "molding" comprehend matched metal die compressionmolds, transfer molds, and injection molds and the process of moldingready-to-mold resin and reinforcement composites in such molds intoreinforced polyester resin thermoset articles. The molding pressuresinvolve range from at least 70 kg/cm² to 110 kg/cm². The term "moldtemperature" means the temprature at the inside surface of the moldwhich forms the finished surface as measured by a pyrometer or the like.The molding tempertures range from at least about 138° C. to 177° C. andabove.

The encapsulated initiators are powdery materials and are used in thesame manner as non-encapsulated initiators. From about one to twopercent by weight of the organic peroxide initiator is used based uponthe weight of the resin in monomer in accordance with the currentpractice. Smaller adjustments must be made, however, for the weight ofthe encapsulating material.

It will be understood that, in accordance with the patent laws, theforegoing examples are by way of illustration and not limitation, andthat various modifications and adaptations of the inventions disclosedherein may be made without departing from the spirit thereof.

What is claimed is:
 1. A process for the manufacture of a molded,reinforced polyester resin polymeric product comprising the steps of:(a)forming by intensively mixing a ready-to-mold resin and reinforcementcomposite of an unsaturated polyester resin reactant, a cross-linkingmonomer, reinforcing material, and microcapsules of from 5 to 200microns in diameter containing a liquid phase including an initiator forcross-linking of the polyester resin reactant and the monomer, saidmicrocapsules isolating said initiator from said resin until apredetermined elevated temperature of at least about 180° C. is reachedin the process; (b) aging said composite until a control viscosity of atleast 60,000,000 centipoises at 22° C. is reached; (c) introducing apredetermined amount of said composite into a cavity of a mold; (d)applying heat and pressure to said composite to fill said mold cavityuniformly with mixture prior to any significant initiator-inducedcross-linking during a first portion of the molding cycle; (e) causingsaid microcapsules to release said initiator at said predeterminedelevated temperature by using the vapor pressure of the liquid phasewithin the microcapsules, and thereby terminating said first portion ofthe molding cycle and commencing a second exothermic portion of themolding cycle, said microcapsules having a wall thickness and strengthsufficient to withstand the vapor pressure of said liquid phase up tothe internal pressure developed in the microcapsules at saidpredetermined elevated temperature; (f) effecting substantially allinitiator-induced cross-linking during said second exothermic portion ofthe molding cycle whereby said first portion of said molding cycle issubstantially prolonged by maintaining said initiator in saidmicrocapsules and the prolongation of the first portion of said moldingcycle permits the use of increased molding temperatures and a netreduction in the overall molding cycle as compared with the use of suchinitiator in the composite in a conventional nonencapsulated form; and(g) removing the cured composite from said mold cavity to provide saidpolymeric product.
 2. The process of claim 1, wherein said microcapsulehas a wall thickness and strength sufficient to withstand pressureswithin said cavity up to at least 70 kg/cm² at said predeterminedtemperature.
 3. The process of claim 1, wherein said ready-to-mold resinand reinforcement composite is a compound selected from the groupconsisting of SMC and BMC.
 4. The process of claim 1, wherein at leastone additive is added to said composite in step (a).
 5. The process ofclaim 1, in which the molding temperature is increased and a netreduction in the overall molding cycle is obtained.
 6. The process ofclaim 1, wherein the predetermined elevated temperature is between 128°and 167° C.
 7. The process of claim 1, wherein said microcapsulesrelease the initiator at a temperature in the range of from about 30° C.below the molding temperature to about the molding temperature.
 8. Theprocess of claim 1, wherein the temperature reached by the composite instep (a) is between 32° and 65° C.
 9. The process of claim 1, in whichthe liquid phase comprises the initiator.
 10. The process of claim 1, inwhich the liquid phase comprises a solvent for the initiator.
 11. Theprocess of claim 1, in which the liquid phase comprises a liquidincluded within the microcapsules to provide the liquid phase.